The present invention relates to a mechanism for generating a flame jet, and more specifically to a two-volume combustion apparatus in which a flame jet is generated and transmitted from one volume into the other, particularly in conjunction with combustion-powered fastener driving tools.
Gas combustion devices are known in the art. A practical application of this technology is found in combustion-powered fastener driving tools. One type of such tools, also known as IMPULSExe2x96xa1 brand tools for use in driving fasteners into workpieces, is described in commonly assigned patents to Nikolich U.S. Pat. Re. No. 32,452, and U.S. Pat. Nos. 4,522,162; 4,483,473; 4,483,474; 4,403,722, 5,197,646 and 5,263,439, all of which are incorporated by reference herein. Similar combustion powered nail and staple driving tools are available commercially from ITW-Paslode of Vernon Hills, Ill. under the IMPULSExe2x96xa1 brand.
Such tools incorporate a generally pistol-shaped tool housing enclosing a small internal combustion engine. The engine is powered by a canister of pressurized fuel gas, also called a fuel cell. A battery-powered electronic power distribution unit produces a spark for ignition, and a fan located in a combustion chamber provides for both an efficient combustion within the chamber, while facilitating processes ancillary to the combustion operation of the device. Such ancillary processes include: inserting the fuel into the combustion chamber; mixing the fuel and air within the chamber; and removing, or scavenging, combustion by-products. The engine includes a reciprocating piston with an elongated, rigid driver blade disposed within a single cylinder body.
A valve sleeve is axially reciprocable about the cylinder and, through a linkage, moves to close the combustion chamber when a work contact element at the end of the linkage is pressed against a workpiece. This pressing action also triggers a fuel metering valve to introduce a specified volume of fuel into the closed combustion chamber.
Upon the pulling of a trigger switch, which causes the spark to ignite a charge of gas in the combustion chamber of the engine, the piston and driver blade are shot downward to impact a positioned fastener and drive it into the workpiece. The piston then returns to its original, or xe2x80x9creadyxe2x80x9d position, through differential gas pressures within the cylinder. Fasteners are fed magazine-style into the nosepiece, where they are held in a properly positioned orientation for receiving the impact of the driver blade.
Upon ignition of the combustible fuel/air mixture, the combustion in the chamber causes the acceleration of the piston/driver blade assembly and the penetration of the fastener into the workpiece if the fastener is present. Combustion pressure in the chamber is an important consideration because it affects the amount of force with which the piston may drive the fastener. Another important consideration the amount of time required to drive the piston and complete the ancillary processes between combustion cycles of the engine. A typical operator of a combustion-powered tool will generally sense a delay when the time required to drive the fastener after pulling the trigger is more than approximately 35-50 milliseconds. There are other types of conventional combustion-powered tools which do not incorporate a fan in the combustion chamber.
Single-chamber combustion systems are effective in achieving a fast combustion cycle time. This type of system, however, does not generally realize peak combustion pressures to drive a piston which are as high as those seen in other gas combustion-powered tools.
One such conventional combustion-powered tool which yields decent peak combustion pressures is a two-chamber system, where at least one of the chambers has a tubular shape and is connected to the second chamber. The tubular shaped first chamber has a tube length L and a diameter D, and the ratio of L/D is known to be high, that is, between two and twenty, and preferably ten. A spark plug is located at one closed end of the first chamber, and the other end of this tubular chamber is in communication with the second chamber via a port. The port connecting the two chambers typically includes a reed valve, which remains normally closed to prevent back flow of pressure from the second chamber into the first tubular chamber.
The first tubular chamber, having a volume V1, operates as a compressor. A fuel/air mixture in V1 is ignited by the spark plug at the closed end of the tubular chamber, and advances a flame front toward the port end of the tube. As the flame front advances, unburned fuel/air ahead of the flame front is pushed into the second chamber, or volume V2, and thereby compresses the fuel/air mixture in V2. As the flame propagates from V1 through the port and reed valve and into V2, the air/fuel mixture in V2 ignites. The ignited gas in V2 thus rapidly builds pressure in V2 and closes the reed valve to prevent loss of pressure back into V1. The greater the compression in V2, the greater will be the final combustion pressure of the system, which is desirable. Longer tubular chambers are thus generally preferred as V1 because longer tubes are known to create greater pre-compression into V2.
Long V1 tubes however, result in longer times between the spark at the closed end of V1 and the ignition of the air/fuel mixture in V2, which is undesirable. In a piston driving tool system, longer V2 ignition time also creates a need for a piston delay mechanism, such that the piston movement will begin immediately prior to where the pressure in V2 builds to a maximum obtainable pressure. A typical two-chamber system can take 35 milliseconds to reach peak pressure in V2 to drive a piston (not including time to complete the ancillary processes), which is about the amount of time where the tool operator will generally sense a delay in the tool""s operation.
Time required to complete the ancillary processes for these two-chamber system tools will add to the noticeable delay experienced by the tool operator. The ancillary process time is also known to be greater for two-chamber systems than in single-chamber systems. The time to complete the ancillary processes becomes even greater as the length of the tubular first chamber V1 increases.
A third known gas combustion system utilizes an xe2x80x9caccelerator platexe2x80x9d placed in a single tubular volume, to effectively divide the volume in two. The accelerator plate itself includes multiple holes for communication between the two volumes, and fuel distribution is provided to both volumes separately through a common fuel supply line with two orifices. An operator of a device employing this system triggers fuel mixing via three-inch actuation. This type of device has been shown to allow repeatable combustion cycling. A drawback to accelerator plate systems, however, is that they tend to be bulky and cumbersome to operate. Also, a volume on one side of the accelerator plate may not be increased without necessarily decreasing the other volume.
The above-listed concerns are addressed by the present mechanism for generating a flame jet, which features solid chamber structure containing a combustible gas. An ignition device ignites the combustible gas at one end of the chamber, creating a flame front which rapidly travels through the chamber to be propelled out the chamber at the opposite end as a flame jet. A fan in the chamber acts to mix the gas in the chamber, as well as create a turbulence which enables the flame front to move more rapidly across the chamber.
More specifically, the present invention provides a mechanism for generating a flame jet which has a volume formed of at least one vertical structure and two opposing horizontal structures. A rotatable fan is located within the volume, and is rotatable in a plane generally parallel to the planes of the horizontal structures. The mechanism also contains an ignition source to ignite a combustible gas contained within the volume, the mechanism being configured for propelling a flame jet outside of the volume.
In another preferred embodiment, the mechanism of the present invention may also serve as the combustion chamber of a two-chamber combustion powered apparatus. The flame jet generated by the mechanism is propelled into a second chamber, which is in communication with the combustion chamber. Pressure generated within the second chamber may then drive a piston device connected to the second chamber.
In a two-chamber system, this mechanism is effective for generating rapid combustion cycles and high pressures in a separate chamber. The mechanism is particularly useful for generating, in a relatively compact geometry, rapid combustions and high pressures that are typically seen in larger and more cumbersome devices.